WMOD00478

• Title: Field Experimentation in Weather Modification
• Date: 3/1/1979
• Weather Modification - Doc Type: Report

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94

.

The statement about "a single anvil" wiping out
cumuli constitutes a description of an intelligible mecha-
nism of faraway losses of rain caused by seeding. This
mechanism appears as a specific development of the C-T
hypothesis of James Hughes, the formulation of which
(and our attempt at verification) was published in 1971.
Whether the anvil mechanism accounts for the ob-
served deficiencies of seeded rainfall is a different ques-
tion, which some future studies may resolve. Our studies
suggested a mechanism of faraway effects of local cloud
seeding (Neyman 1975) that is more complex than the
"orphan anvil" mechanism of Simpson and Dennis. Un-
doubtedly, what is intelligible and what is not is a very
subjective matter. A degree of confluence with the ideas
of E.J. Workman, a noted cloud physicist, appears en-
couraging. I regret that for a long time I overlooked his
inspiring article (Workman 1962).
Braham's Table 1 illustrates three points: (a) the
brevity of the information in his article, (b) the practical
consequences of Braham's philosophy, and (c) a differ-
ence between his and my interests in weather modifica-
tion experiments. The information on Whitetop which I
miss in Table 1 is published in Braham and Flueck
(1970), from which I quote two unambiguous state-
ments. One of them reads, "the amount of rain was
distinctly less in the P and NP on seeded days than on
non-seeded days . . ." [here P and NP denote plume and -
nonplume]. It is this finding that causes my regrets about
Braham's persistence in using the non plume as a "con-
trol" area. This finding is not reflected in Braham's
Table 1, "Abbreviated Summary of Project Whitetop
Seeding Results."
The other .unambiguous assertion is: "The observed
differences were substantially larger during the [five]
hours immediately following seeding (-59 to -46%)
than during the 6 seeding hours (-20 to -10%)."
While periods of five and six hours arc mentioned in
Table 1, their relation is not. This fact appears to indicate
a difference between Professor Braham's interests and
mine. I find it curious that, having found that the "post-
seeding" five-hour effects are stronger than those during
the six "seeding hours," Professor Braham was not
tempted to investigate the apparent effects of seeding
that may have occurred during a substantial number of
hours after the end (at 9 P.M.) of the investigated post-
seeding period.
Our own interests are very different. Because of the
clear purpose of cloud seeding in water-deficient regions,
we tend to study the whole experimental unit, such as
24 hours, and we are interested in the whole geographical
area where the effects of seeding can be detected.
In his penultimate paragraph, Braham writes, IISome
statisticians have stated that the lack of randomization

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Journal of the American Statistical Association, March 1979

makes it impossible to evaluate' these projects [nonran-
domized operations]. Is this view accepted by most
statisticians"? Earlier, on three different occasions,
Braham refers to an article by John W. Tukey (1977).
This a.rticle begins with the following passage:

The pressures of ethics and equity on clinical trials have always
been severe. Today they are more vigorous than every before.
Mcmy of us are convinced, by what seems to me very strong
evIdence, that the only 80urce of reliable evidence about the use-
fulness of almost any sort of therapy or surgical interventicm is
thllt obtained from well planned and carefully conducted random-
ized, and when pollSible, double blinded clinical trialB. .. (Em-
phasis added.)

My own opinion is similar (Neyman 1977a, b).

REFERENCES

Braham, Roscoe R., Jr. (1965), "Project Whitetop-Report to the
National Science F'oundation," Department of Geophysical
Sciences, University of Chicago.
- (1966), "Final Report of Project Whitetop," Parts I and II,
mimeographed publieatioIl, Department of Geophysical Sciences,
University of Chicago.
-, and Flueck, John A. (1970), "Some Results of the Whitetop
Experiment," Proceeding8 of the Second National Cunference un
Wea.ther Modification of the A merican Meteorological Society, Santa
Bar~~bara, California.
Lovasich, Jeanne L., Neyman, Jerzy, Scott, Elizabeth L., and Smith,
Jerome A. (1969), "Wind Directions Aloft and Effects of Seeding
on Precipitation in the Whitetop Experiment," Proceeding8 of the
NatiOnal Academy of Science8, 64, 810-817.
-', Neyman, Jerzy, Scott, Elizabeth L., l~nd Wells, Marcella A.
(1971a), "Further Studies of the Whitetop Cloud-Seeding Experi-
ment," Proceedings of the National Academy of ScienceB,' 68,
147..151.
-, Neyman, Jerzy, Scott, Elizabeth L., and Wells; Marcella A.
(1971b), "Hypothetical Explanations of the Negative Apparent
Effects of Cloud Seeding in the Whitetop Experiment," Proceedings
of the National Acadl1my of Sciences, 68, 2643-2646.
Neyman, Jerzy (1975), "Problems of Design and of Evaluation of
Rain Making Experiments," in A Survey of Statistical De8ign and
Linear Models, ed. J.N. Srivastava, Amsterdam: North-Holland
Publishing Co., 443-458.
-- (197790), "A Statistician's View of Weather Modification
Technology (A Review)," Proceeding8 of the National Academy of
Science8, 74, 4714-4121.
-- (1977b), "Experimentation with Weather Control and St&-
tistical Problems Genera.ted by It," in Applicati0n8 of StatiBtic8, ed.
P.R. Krishnaiah, Amsterdam: North-Holland Publishing Co.,
1-25.
--, and Scott, Elizabeth L. (1967), "Note on Techniques of
Ev~Juation of Single Rain Stimulation :Experiments," in Pro-
ceeding8 of the Fifth Berkeley Symp08ium un Mathematical 8ta-
tiBtiu and Probability, V, Berkeley: University of California Press,
371--384.
--, and Scott, Elizabeth L. (1971), "Outlier Proneness of Phe-
nomena and of Related Distributions," in Optimizing M ethod8 in
S~~iBtic8, ed. Jagdish S. Rustagi, New York: Academic Press,
413-430.
Simps:on, Joanne, and Dennis, Arnett S. (1974), "Cumulus Clouds
and Their Modification," in Weather and Climate Modification, ed.
W.N. Hess, New York: John Wiley & Sons, 22~281.
Tukey, John W. (197'7), "Some Thoughts on Clinical Trials, Espe-
cially Problems of Multiplicity," Science, 198,679-684.
Workman, E.J. (1962), "The Problem of Weather Modification,"
Sci.mce, 138, 407-412.